Already the longest-lived of the 45 men to serve as U.S. president, Jimmy Carter is about to reach the century mark.

Already the longest-lived of the 45 men to serve as U.S. president, Jimmy Carter is about to reach the century mark.

America's oldest living president turns 100 years old on Tuesday. Jimmy Carter held office for a single term in 1976, and became even more famous as a global ambassador of goodwill. Birthday tributes have already started,

Carter has seen the U.S. population nearly triple. The U.S. has about 330 million residents; there were about 114 million in 1924 and 220 million when Carter was inaugurated in 1977. The global population has more than quadrupled,